Utilization of converter waste heat
Amprion has developed a concept to make effective use of the waste heat generated in converters on high voltage direct current (HVDC) transmission lines. The term “waste heat” refers to thermal energy generated as a byproduct of technical processes—for example, during steel production, in data center cooling systems, or during coal combustion in a power station. Reusing this energy instead of releasing it unused into the environment is both sustainable and required by law. The potential applications are diverse, such as for cost-effective heating of municipal swimming pools or as a supplementary feed in to local district heating networks.
Amprion also builds and operates operating facilities and assets suitable for waste heat utilization. Converters in HVDC lines are the primary example here. They are necessary to convert direct current to alternating current at the line endpoints. Waste heat is also generated during this process.
How the thermal energy is to be extracted
Here’s how the concept works: To extract the thermal energy, a heat exchanger is required. With its help, a separate water circuit is connected to the existing converter cooling system. This water circuit can either be integrated during the initial installation of the asset or, with appropriate preparation, retrofitted at a later date. This provides flexibility and avoids uncertainties in the planning of the HVDC system. The additional components required, such as heat exchangers, pumps, and filters, are installed in a separate building or container.
In the water circuit for heat extraction, a large tank is installed as a hot water storage tank, which offers various operational advantages. A supply line and a return line run from the hot water storage tank to the interconnection point. This is located outside the Amprion premises. The lines are laid underground. The heat consumer connects to these pipes and is also responsible for the operation of the pipes from the interconnection point onward. Rights and obligations regarding the technical interface are governed by a corresponding contract.
Heat output depends on the project
The amount of heat supplied is measured near the interconnection point. How much heat can be expected? Important: This depends on the specific converter. For the converter planned for the BalWin1 offshore grid connection system, the average energy yield is estimated at approximately 25 GWh/year.
However, deviations of around six GWh/year in either direction are to be expected. This depends on the amounts of electricity generated, and thus ultimately on wind conditions over the course of the year. In principle, the smooth operation of the converter takes precedence over heat extraction.
When will waste heat recovery begin?
The converters for the BalWin1 and BalWin2 offshore grid connections are set to kick off waste heat utilization as pilot projects. Amprion is connecting offshore wind farms in the North Sea to the power grid via these two DC lines. The converter for BalWin1 is to be built in the municipality of Bohmte (Osnabrück district), and the converter for BalWin2 on the site of the former coal-fired power station in Ibbenbüren (Steinfurt district). They are scheduled to go into operation in 2030 and 2031, at which point waste heat would also become available.
Amprion is therefore currently examining options for marketing the waste heat to third parties at the Bohmte and Ibbenbüren sites. The market exploration process was recently completed. The tender for the waste heat is scheduled for 2026.